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PUBLIC !lEALTH SERACES <br /> SAN JOAQUIN COUNTY <br /> r. ? <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Ernest M. Fujimoto, M. D., M.P.H., Acting Health Officer , <br /> 304 E. Weber Ave., Third Floor • P. O. Box 388 • Stockton, CA 95ib1-0388 • c4iiFORa P <br /> 209/468-3420 _ <br /> TINA BERRY SEP 13 0 199 <br /> UNOCAL CORPORATION <br /> 2000 CROW CANYON PLACE STE 400 <br /> SAN RAMON CA 94583 <br /> RE: UNOCAL SS#5098 (former) SITE CODE: 2163 <br /> 5606 Pacific Ave. <br /> Stockton, CA 95207 <br /> 1 have reviewed your letter of August 15, 1996 in response to my letter of June 14, 1996 <br /> and I will offer these comments. <br /> Fluctuating groundwater flow directions at this site have presented situations that have <br /> caused much speculation as to the source of the consistently high groundwater <br /> contaminant levels detected in MW-11, MW-12 and Montgomery Ward's (Ward's) <br /> MW-3. <br /> On March 11, 1996, the groundwater was at the highest level ever recorded on these <br /> sites (DTW/ MW-11= 43.22 feet below ground surface (bgs), nearly eight feet over the <br /> top of the screen) and flowed easterly. On March 11, 1996, Ward's MW-3 reported the <br /> highest concentrations of TPH-G (86,000 ug/1) and Benzene (15,000 ug/1) for both sites. <br /> Unfortunately, this was also the time UNOCAL chose to alter their sampling frequency <br /> and not sample MW-11 and MW-12, and as a result, no accurate conclusion may be <br /> reached as to the dilution pattern as I referred to in my June 14 letter. <br /> On June 19, 1996, the groundwater receded to 45.41 feet in MW-11 and the <br /> groundwater flow was in the southwesterly direction. Ward's MW-3 again showed the <br /> highest concentration for the two sites with TPH-G at 90,000 ug/I and Benzene at <br /> 16,000 ug/I. <br /> With the highest concentrations in a well that is up-gradient of any known Ward's <br /> sources and down-gradient-to-laterally-gradient to UNOCAL's known sources, I am <br /> convinced that the continuing source to this plume has not been identified. <br /> Also unclear is the consistently large difference in contaminant values between MW-11 <br /> (TPH-G = 36,000 ug/I on June 19, 1996) and MW-12, (TPH-G = 2,500 ug/I on June 19, <br /> 1996) when these wells are less than 40 feet apart. Both of these wells are about 60 <br /> A Division of San Joaquin Counts Health Care Services <br />